In high bandwidth optical transport networks, recent standards such as ITU-T Recommendation G.709 “Interfaces for the optical transport network” (June 2016), the contents of which are incorporated by reference, describe the use of multiple optical carriers for a single digital transport interface in line side applications, such as an Optical Transport Unit-Cn (OTUCn) which is carried via multiple Optical Tributary Signal (OTSi) carriers (lambdas). OTSi is described in G.959.1 “Optical transport network physical layer interfaces” (April 2016), the contents of which are incorporated by reference, as an optical signal that is placed within a Network Media Channel (NMC) for transport across the optical network. This may include a single modulated optical carrier or a group of modulated optical carriers or subcarriers. For client-side applications, ITU-T Recommendation G.709.1 “Flexible OTN short-reach interface” (January 2017) the contents of which are incorporated by reference and future ITU-T Recommendation G.709.3 “FlexO for longer reach interfaces,”, define the use of multiple client services/modules for a single OTUCn transport service. Similarly, the Optical Internetworking Forum (OIF) has worked on IA # OIF-FLEXE-01.1 “Flex Ethernet Implementation Agreement” (June 2017), the contents of which are incorporated by reference, for FlexE to transport an Ethernet client service across multiple standard rate client interfaces/servers.
Timing synchronization between nodes in a network is described in various standards such as IEEE 1588-2008 “Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems,” ITU-T G.8265.1/Y.1365.1 (July 2014) “Precision time protocol telecom profile for frequency synchronization,” ITU-T G.8275.1 “Time and Phase Profile,” the contents of each is incorporated by reference herein. The requisite information for the transfer of precise time is (1) a time reference point, or “significant instant” to which timing information can be related, (2) the timing information itself, and (3) a measure of the delay it takes to transfer the timing information between two nodes. IEEE 1588-2008 is referred to as Precision Time Protocol (PTP) and is used to synchronize time (frequency and phase) throughout the network. IEEE 1588-2008 only defines a protocol for transferring time information over a packet network. In general, PTP supports accuracy in the sub-microsecond range.
For example, 2×OTSi in an OTSiG (OTSi Group) has two physically independent optical carriers which are transported in the network, but which are logically part of the same group. There is a need to deskew OTSi due to differences in light propagation speed, chromatic dispersion, etc. For creating 2×OTSi into an OTSiG (OTSi Group), most solutions (e.g., Digital Signal Processing (DSP) Application Specific Integrated Circuit (ASIC)) are built in an integrated manner, e.g., in a single die or package. As such, sharing a common time base for deskewing and alignment purposes is less complex were all members of the group are collocated on the same physical device. Since their OTSi members are physically separate signals but treated logically as a group, there is a requirement to deskew these signals to ensure all signals have the same time base.